The present invention relates to a new process for the preparation of telechelics based on vinyl polymers, the telechelics prepared in this way and their use in the plastics, fibers or coatings sector.
Linear oligomers or low molecular weight linear polymers with functional groups on both chain ends are in general called telechelics. A comprehensive overview of the preparation of telechelics is to be found in Adv. Polym. Sci., 1987, 81, 168. They have acquired importance inter alia as additives and as building units (prepolymers) for higher molecular weight copolymers of defined structure (block copolymers, comb polymers, star polymers). An exact bifunctionality is necessary in particular for use of telechelics as building units for copolymers. The most widely known reactions for the preparation of telechelics having an exact functionality of 2 are polyaddition reactions (to give polyurethanes or polyureas), polycondensations (to give polyesters, polycarbonates or polyamides) and ring-opening anionic or cationic polymerizations of heterocyclic monomers (cyclic esters, carbonates, acetals or ethers). Optionally these reactions are performed with termination reagents which contain the desired functional groups.
Telechelic polyacrylates, i.e. linear oligomers of acrylates or low molecular weight acrylate polymers or copolymers with two defined functional end groups which can participate in the crosslinking, chain lengthening and/or coupling reactions conventionally used in coating chemistry, are of great interest for use in the coating industry.
However, these telechelic polyacrylates cannot be prepared by any of the processes described above for the preparation of telechelics.
Various methods are known in polymer chemistry for providing polyvinyl or poly-acrylate compounds with functional end groups. Oxidative chain cleavages (with oxygen, ozone and osmium tetroxide or ruthenium tetroxide) proceed non-specifically and/or require double bonds in the polymer chains as the point of the cleavage. An exact bifunctionality can scarcely be achieved in this way.
The same problem occurs in a free radical polymerization. If a content of monomers which carry the desired functional group calculated for a functionality of two is used, a product mixture is obtained which has only an average functionality of two. Bi-functional molecules are present alongside trifunctional and more than trifunctional, monofunctional and also non-functional polymer molecules. This is based on the statistical character of free radical polymerization and on an influence of the various termination reactions which is difficult to control.
If initiators and/or termination reagents which carry the desired functional groups (functionalized diazo compounds, functionalized peroxides or redox initiators) are employed instead of the monomers carrying functional groups, a functionality of 2 is in general not achieved because the ratio of the competing termination reactions. Disproportionation, recombination and termination cannot be controlled in a targeted manner by initiator radicals or the termination reagent. In so-called xe2x80x9cdead end polymerizationxe2x80x9d, a large excess of an initiator having the desired end group is used so that practically every polymer chain is terminated by an initiator molecule and is thus bifunctional. Only very low molecular weights are achieved in this way and the products formed become uneconomically expensive because of the large amounts of initiator.
In the case of telomerization, i.e. the polymerization of vinyl or acrylate monomers in the presence of chain transfer reagents with high chain transfer constants, likewise only low molecular weights are achieved, and the use of this remains limited to a few cases (polymerization in the presence of carbon tetrachloride, dibromomethane or disulfides carrying functional groups). Since disproportionation as a termination reaction between two active chain ends cannot be suppressed entirely, functionalities of the telechelics of less than 2 are found. In the case of halogen compounds at least, subsequent polymer-analogous reaction of the halogen substituents to give the desired functional groups is also necessary.
Telechelic polymethacrylates can be prepared by group transfer polymerization with ketene silyl acetals, the functional end group being formed by conversion of the silyl groups. However, disadvantages here are the high purity requirements on the monomer and solvent and the price and availability of the initiators required, which means that such a process would be applicable only for special applications.
It is known from EP-A 613910 and EP-A 622378 to prepare xcex1,xcfx89-polymethacrylate diols by selective transesterification of the terminal ester group of an xcex1-hydroxy-functional polyalkyl methacrylate. This process has several disadvantages. On the one hand, the xcex1-hydroxy-functional polyalkyl methacrylate is prepared by free radical polymerization in the presence of large amounts of mercaptoethanol, which is associated with a considerable odor nuisance. On the other hand it is a multi-stage, energy- and time-consuming process which comprises distilling off the excess mercaptoethanol and the solvent used, transesterification with an excess of a diol in the presence of a catalyst, removal of the methanol by distillation, washing of the product several times to remove the catalyst and the excess diol and other purification steps. Furthermore, this reaction remains limited to the exclusive use of alkyl methacrylates, since otherwise the transesterification reaction no longer proceeds sufficiently selectively on the terminal ester group of the chain.
Ring-opening polymerization of unsaturated heterocyclic compounds is also a special case without a wide application and economic potential (cyclic ketene acetals or unsaturated spiroorthocarbonates); such monomers are not available industrially.
None of the methods described so far is therefore suitable for the preparation of the desired telechelic polyacrylates, since either the required functionality is not achieved, the method remains limited to only a few special cases and/or polymer-analogous after-reactions are necessary. A polymerization process which allows a good control of the polymerization and in particular of the end groups of the polymer chains, while being easy to carry out, is needed. Such a process is living free radical polymerization.
Living free radical polymerization is a relatively young method of controlled free radical polymerization. It combines the advantages of a conventional free radical polymerization (simple synthesis process, inexpensive, broad monomer base) with those of a living polymerization (polymers of defined structure/molecular weight and distribution and end group functionality). The aim of precise control of free radical polymerization is achieved here by a reversible chain termination or blocking (xe2x80x9cend-cappingxe2x80x9d) after each growth step. The equilibrium concentration of the polymerization-active chain ends is so low here in comparison with the equilibrium concentration of the blocked (xe2x80x9cdormantxe2x80x9d) chain ends that termination and transfer reactions are severely suppressed compared with the growth reaction. Since end-capping proceeds reversibly, all the chain ends remain xe2x80x9clivingxe2x80x9d if no termination reagent is present. This allows control of the molecular weight, a low polymolecularity index and controlled functionalization of the chain ends by termination reagents.
Controlled free radical polymerization using tetraalkylthiuram disulfides is described by Otsu et al. (Makromol. Chem., Rapid Commun. 1982, 3, 127-132). The preparation of telechelics having functional groups capable of a further reaction or crosslinking with functional groups used in coating chemistry is not disclosed.
Atom Transfer Radical Polymerization (ATRP) is a method, in which a transition metal complex compound MLx abstracts a transferable atom or atomic group X (Cl or Br) from an organic compound RX to form an oxidized complex compound MLxX and an organic radical Rxe2x80xa2, which adds on to a vinyl monomer Y to form the carbon radical RYxe2x80xa2. This radical can react with the oxidized complex compound with transfer of X to give RYX and MLx, which can trigger off a new ATRP and therefore another growth step. The polymerization-active species RYxe2x80xa2 is thus blocked reversibly by the abstractable group X with the aid of the transition metal compound, which renders the redox process possible.
This method is described inter alia by Sawamoto et al (Mxe2x95x90Ru, Xxe2x95x90Cl; Macromolecules 1995, 28, 1721; Macromolecules 1996, 29, 1070), Percec et al. (M⊚Cu, RXxe2x95x90arylsulfonyl halide); Macromolecules 1995 28, 7970), Du Pont (Mxe2x95x90Co (inter alia), Rxe2x80xa2 from Rxe2x80x94Nxe2x95x90Nxe2x80x94R; WO 95/25765) and in particular by Matyjaszewski et al. (WO 96/30421 and WO 97/18247). In the latter documents, (co)polymers with one or two functional end groups are also described, these end groups being formed in a polymer-analogous manner from the halide end groups which are initially present. However, this method has the disadvantage that for preparation of the desired telechelics, one or more reaction steps are still necessary after the actual polymerization reaction in order to convert the halide groups into the desired functional groups, while other groups, such as the ester groups of the acrylate monomers, must remain untouched. The ATRP process also has the disadvantage that the polymers must be separated from the catalyst system used (Cu, bipyridine) by an expensive purification process. Residues of Cu impair the color and other properties of the polymers obtained.
U.S. Pat. No. 4,581,429 discloses alkoxyamines which are formed by reaction of linear or cyclic nitroxides, such as 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO), with organic carbon-based free radicals, and a process for the preparation of vinyl polymers using these initiators. At temperatures  greater than 100xc2x0 C., the Cxe2x80x94ON bond can be cleaved reversibly to re-form the C radical (xe2x80x9cactive speciesxe2x80x9d) and the stable nitroxide radical. The equilibrium lies far on the side of the alkoxyamine (xe2x80x9cdormant speciesxe2x80x9d). The result of this reaction is a low, stationary, free radical concentration which, in the case of free radical polymerization of vinyl monomers, means that bimolecular termination reactions are kinetically unfavorable compared with the unimolecular growth reaction. Side reactions are thus largely suppressed and a xe2x80x9clivingxe2x80x9d reaction procedure becomes possible for the free radical polymerization. Hydroxy-functional end groups are described by polymer-analogous reductive splitting of the TEMPO end groups with Zn/acetic acid.
The preparation of vinyl polymers by living free radical polymerization (xe2x80x9cStable Free Radical Polymerizationxe2x80x9d, SFRP) on the basis of alkoxyamines is described by Hawker et al. (J. Am. Chem. Soc. 1994, 116, 11185; Macromolecules 1995, 28, 2993) and Georges et al. (Xerox Comp., U.S. Pat. Nos. 5,322,912, 5,401,804, 5,412,047, 5,449,724, WO 94/11412, WO 95/26987 and WO 95/31484). The carbon radicals are prepared by addition of free radical initiators (peroxides, azo initiators) on to monomers which can be polymerized by free radicals; these free radicals are then captured in situ by TEMPO to give alkoxyamines. These alkoxyamines are the actual initiators, since they are split reversibly into free radicals at temperature  greater than 100xc2x0 C. and in this way can initiate the polymerization of the monomers metered in. During the polymerization, the number of growing chains (and therefore the molecular weight) is then determined by the concentration of the alkoxyamine initiators. Compared with ATRP, this polymerization process offers the advantage of the absence of metals, i.e. the expensive step of separating off the Cu catalyst and its reaction products is omitted here. Difunctional telechelics have previously been obtained only by chain-analogous reactions (oxidative splitting off of the TEMPO end group). The synthesis of polyacrylate telechelics, the functional groups of which are capable of a further reaction or crosslinking with the known functional groups coatings chemistry, by using difunctional alkoxyamine initiators has not previously been described.
WO 97/46593 describes the preparation of hydroxytelechelic butadiene polymers by SFRP. The polymerization of butadiene is carried out in the presence of H2O2 and TEMPO in a polar solvent. H2O2 reacts as an initiator and as a termination reagent. Oligomers of  less than 3.000 with a polymolecularity index of 1.3-3.4 and OH functionalities of 0.59-1.69 are obtained. The use of functionalized alkoxyamine initiators and/or acrylate monomers or styrene is not described here.
The use of alkoxyamine initiators which additionally carry functional groups which are capable of a further reaction or crosslinking with the known functional groups coatings chemistry for the preparation of telechelic polyacrylate copolymers is not described in any of the documents or processes of the prior art mentioned.
An object of the present invention is to provide a process for the preparation of telechelics which does not have the disadvantages of the prior art. In particular, a process is sought which allows the preparation of a homo- or copolymer of one or more vinyl monomers, in particular acrylate monomers, and styrene, in a simple manner and to the effect possible in a one reaction step reaction without subsequent purification. The molecular weight should be established in a controlled manner and a low polymolecularity index (polydispersity) and two functional end groups (Y, OH) should be achieved, wherein Y represents a functional group which is reactive with isocyanates, alcohols, carboxylic acids, anhydrides and/or epoxides. The resulting polymer should also have a thermal stability of  greater than 200xc2x0 C. that is adequate for processing.
The present invention relates to a process for the preparation of telechelics of the formula HOxe2x80x94Bxe2x80x2xe2x80x94Qxe2x80x94Bxe2x80x3 or HOxe2x80x94Bxe2x80x2xe2x80x94Gxe2x80x94Cxe2x80x94Bxe2x80x2xe2x80x3 having a molecular weight 200 less than Mn less than 50.000, wherein Q is represented by the formula 
wherein
n is an integer in the range 3xe2x89xa6nxe2x89xa6500 and
Rxe2x80x2, Rxe2x80x3 and Rxe2x80x2xe2x80x3 are the same or different and represent H, C1-C20-(cyclo)alkyl, C6-C24-aryl, halogen, CN, C1-C20-cycloalkyl ester or -amide or C6-C24-aryl ester or -amide, can also contain further substituents, such as ether groups, and can also be a constituent of a ring structure, in a cyclic anhydride, ester, amide or hydrocarbon, and
which comprises reacting
A) monomers A, which can be polymerized by free radicals, of the formula
CHRxe2x80x2xe2x95x90CRxe2x80x3Rxe2x80x2xe2x80x3
with
B) a functionalized alkoxyamine initiator B of the formula I: 
wherein
[xe2x80x94CR1xe2x80x94CR2R3xe2x80x94] represents Bxe2x80x2,
R1, R2 and R3 are the same or different and represent H, C1-C20-(cyclo)alkyl, C6-C24-aryl, halogen, CN, C1-C20-(cyclo)alkyl ester or -amide or C6-C24-aryl ester or -amide, and
[xe2x80x94Oxe2x80x94NR4R5] represents Bxe2x80x3/Bxe2x80x2xe2x80x3,
R4 and R5 independently of one another represent aliphatic, cycloaliphatic or mixed aliphatic/aromatic radicals having 1-24 carbon atoms, which can also be part of a 4- to 8-membered ring, wherein the carbon atom of the radicals R4 and R5 directly adjacent to the alkoxyamine nitrogen atom is in each case substituted by 3 further organic substituents (other than hydrogen) or a double-bonded carbon, oxygen, sulfur or nitrogen atom and a further organic substituent (not hydrogen), and
in case of Bxe2x80x3
at least one of the radicals R4 and R5 contain a functional group Y,
Y represents a functional group which is reactive with isocyanates, alcohols, carboxylic acids, anhydrides and/or epoxides
and
optionally
C) a functionalizing reagent C of the formula R14R15Cxe2x95x90CR16(R17xe2x80x94Y),
wherein R17 represents a linear or branched, optionally substituted alkyl chain with a minimum length of 1 methylene group and
R14, R15 and R16 independently of one another represent hydrogen or an optionally aryl- or halogen-substituted alkyl radical.